Configuration Details:

When this is 'on', a request will not go through the
helper if all helpers are busy. If this is 'off' and the helper
queue grows too large, the action is prescribed by the
on-persistent-overload option. You should only enable this if the
helpers are not critical to your caching system. If you use
helpers for critical caching components, and you enable this
option, users may not get objects from cache.
This options sets default queue-size option of the store_id_children
to 0.